Gut Bacteria And Mental Health

What you eat may control how you think, according to new study reports. It has been found that two different gut bacteria are depleted in people with depression, regardless of antidepressant treatments. They discovered this from the first population-level study on the link between gut bacteria and mental health, specifically quality of life and depression.

Apart from identifying specific gut bacteria linked to depression, the research also provides evidence that a wide range of gut bacteria can produce neuroactive compounds. Jeroen Raes (VIB-KU Leuven) and his team published these results in the scientific journal Nature Microbiology.

Prof Jeroen Raes (VIB-KU Leuven) said:

“The relationship between gut microbial metabolism and mental health is a controversial topic in microbiome research. The notion that microbial metabolites can interact with our brain – and thus behaviour and feelings – is intriguing, but gut microbiome-brain communication has mostly been explored in animal models, with human research lagging behind. In our population-level study we identified several groups of bacteria that co-varied with human depression and quality of life across populations.”

The Research:

• Faecal microbiome data was combined with general practitioner diagnoses of depression from 1,054 individuals enrolled in the Flemish Gut Flora Project.
• From this, the team identified specific groups of microorganisms that positively or negatively correlated with mental health by using bioinformatics analyses.
• Then, they checked their results by doing the same thing with another cohort of 1,063 people involved in a similar study in the Netherlands and found the same result.

The Findings:

• Two bacterial genera, Coprococcus and Dialister, were consistently found to be at low numbers in individuals with depression, regardless of antidepressant treatment.

Gut Bacteria And The Nervous System

Some bacterial species in the microbiome may be able to produce or breakdown molecules that interact with the human nervous system. The researchers discovered this by looking at bacterial DNA from fecal samples in a subset of the study group. They found that the gut microbiome may be able to synthesize molecules such as serotonin and dopamine, which are found in abnormal levels in people with depression. People with treatment-resistant depression had microbiomes that were less likely to be able to synthesize these molecules than healthy people.

Mireia Valles-Colomer (VIB-KU Leuven) said:

“Many neuroactive compounds are produced in the human gut. We wanted to see which gut microbes could participate in producing, degrading, or modifying these molecules. Our toolbox not only allows to identify the different bacteria that could play a role in mental health conditions, but also the mechanisms potentially involved in this interaction with the host. For example, we found that the ability of microorganisms to produce DOPAC, a metabolite of the human neurotransmitter dopamine, was associated with better mental quality of life.”

What’s Next?

Jeroen Raes and his team are now preparing another sampling round of the Flemish Gut Flora Project. He says there is still lots of work to be done and there are many questions left unanswered. For example, “we don’t yet know whether these neuroactive compounds produced in the gut can reach the brain. Can they traverse the blood-brain-barrier? Or perhaps they act directly on the vagus nerve in the intestines, which sends signals directly to the brain.”

No matter what, the large number of people involved in the study, and the analysis methods used, make this research a formidable piece of work to show that the microbiome is likely related to mental health. His teams analyses will surely help direct and accelerate future human microbiome-brain research.

What they have to do next is confirm these findings experimentally. Raes says:

“Our goal would be to isolate these specific bacteria and culture them in animal models to see if they elicit or change behavioral traits. If this is proven then they next step would be to set up human trials to see if procuring these bacteria can improve symptoms in people with depression.”

In conclusion, Raes mentions that, “At this moment there is not enough evidence to say that modulating the microbiome is a treatment for depression. However, general healthy advice never hurts. The gut microbiome is always helped by a good diet full of fibre and lots of varied fruits and vegetables.”

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